Method of vulcanizing rubber and resulting products



Patented Nov. 5, 1929 HENRY IB. MORSE, OF DANVERS, MASSACHUSETTS, ASSIGNOR, BY MESNE ASSIGNMENTS T ALBERT C. BURRAGE, JR., OF IPSWICH, MASSACHUSETTS I METHOD OF VULCANIZING RUBBER ANlJ RESULTING PRODUCTS NoDrawing. I Application filed June 4,

This invention relates to the art of treating rubber or rubber compounds, and has for an object the provision of an improved procedure for the vulcanization of the same in the presence of an accelerator and of compounds or compositions with which to effect the purpose of the invention.

-In the art of rubber manufacture, it has long been known that the vulcanizing process may be, accelerated by the addition of various compounds in relatively small amounts. The compounds which have been found-to thus accelerate vulcanization, known as accelerators, have been constantly added to by research and mow include numerous types of substances, both inorganic and organic. Of these substances, the organic compounds are preeminently the more satlsfactory and present a wide range of accelerating activity. Those selected for practical use, however, are generally restricted to-compounds which may be mixed with the rubber or rubber compound without inducing appreciable vulcanizing effect at atmospheric temperature or during milling operations, but which actively accelerate the reaction in the customary vulcanizing treatment. Other accelerator compounds, frequently termed ultra accelerators or semi-ultra accelerators, initiate the vulcanizing reaction sometimes prematurely, either in the cold or during the mixing 0 eration, resulting in scorching which hin ers or entirely prohibits the further use of the rubber or rubber compound. 5 Consequently, such compounds ordinarily have not been used in the manufacture of rubber products, even though they would greatly reduce the time required for vulcanization and may be otherwise suitable 4 for use in rubber compositions.

By the present invention it is found that the accelerating action of accelerator compounds generally in rubber compositions, may be in- 1929. Serial No. 368432.

ing operations) or retarded by the addition of organic compounds of a certain type hereinafter defined, and that thereafter the vulcanizing reaction, effectively accelerated by the accelerat0r,--may be caused to proceed at will by subjecting the rubber composition to be vulcanized to vulcanizing conditions.

It is thought that the accelerator and the inhibitor react or combine to form a reaction product or compound which does not promote the vulcanizing reaction of the vulcanizable composition (under the preliminary conditions such as mixing and milling) but which, under the vulcanizing conditions such as increased temperature, diassociates and liberates the accelerator which then acts in its accelerating capacity, and the inhibitor may remain inert or may itself act as an accelerator.

In other words, the critical temperature of the accelerator, with respect to its initiattimes referred to as semi-ultra aocelera-' tors-among which may be mentioned the thiazoles, represented by mercapto benzo thiazole, certain disulphldes such as tetra methyl thiuram disulphide, certain monosulphides such as tetra methyl thiuram monosulphide, etc., and their derivatives) are found to typically include the nitroso-amines which may be represented by the empirical formula 2- t I in which R and R"-represent alkyl or aryl radicals (or nuclei) which may be alike or unlike and in turn may contain or be associated with one or more substituents.

For example, the aryl radicals or nuceli R and R or either of them, may contain further substitutions which are preferably monovalent such as the alkyl hydrocarbons of which the methyl group is representative, in phenyl paratolyl nitrosoamine.

In a representative example of the invention, rubber and the usual vulcanizing and filler materials, together with the desired amounts of the accelerator compound and inhibiting compound, may be compounded and mixed in the usual manner as by milling (without premature vulcanization or scorching), and subsequently molded and. vulcanized to the required degree of cure, by heating to the usual range of vulcanization temperatures. The rate of vulcanizationand degree of cure obtained may be accurately controlled by the time and temperature of vu 1- canization, to provide a final cure equal to or better than that obtained without the use of the preliminary inhibiting compound or prehibitor.

In a preliminary scorching test, for example, in which the compounds were subjected to especially high temperatures during the mixing and milling operations until scorching was effected, a rubber composition containing:

100 parts rubber (smoked sheet) 3 parts sulphur 5 parts ZnO A part mercapto benzo thiazole to which .43 part dibeta naphthyl nitrosoamine was added, was thoroughly milled and mixed on the mixing rolls; the mix was then removed and again milled on rolls, purposely heated by steam so as to maintain a temperature in the stock of approximately 95 to 100 C.,for 110 minutes before scorching occurred.

A corresponding stock without the addition of dibeta nephthyl nitroso-amine, upon being mill-ed and mixed, and again milled under like conditions of temperature, scorched in minutes.

A similar test carried out upon a rubber compound of the formula:

100 parts rubber (smoked sheet) 3 parts sulphur 5 parts ZnO .15 part tetra methyl thiuram disulphide .75 part dibeta naphthyl nitrosc-amine pjroduced scorching in about 72 minutes. nder like conditions the same compound, without the dibeta naphthyl nitroso-amine, was scorched in twenty minutes.

A third compound, having the formula:

100 parts rubber (smoke sheet) 3 parts sulphur 5 parts ZnO .15 part tetra methyl thiuram monosulphide 1 .75 part dibeta naphthyl nitroso-amine was treated in the same way as the preceding compounds and scorching took place in'118 minutes, while the same compound, without dibeta-naphthyl nitroso-amine, was scorched in about 65 minutes, under the same conditions.

This test, developed for the purpose, serves to measure the'degree of the retarding or inhibiting effect of the inhibiting compound upon the vulcanization reaction and the accelerating influence of the ultra accelerator at temperatures of about 100 C. or less, as

contrasted With vulcanizing temperatures which as ordinarily employed are above 120 C.

Similar tests were carried out employing the same composition, but with a different lot of smoked sheet rubber which tended to scorch slower (without the addition 'of prehibitor) than the rubber employed above. The results obtained are given below:

In a typical application of the invention to the usual vulcanizing procedure, rubber compounds were prepared as follows:

I parts rubber 40.5 parts carbon black 5.0 parts ZnO 3.0 parts sulphur 5.0 parts mineral rubber 3.0 parts stearic acid .8 pr rt mercapto benzo thiazole part diphenyl nitroso-amine.

A B C D Same as formula I with addition of .50 part dlphenyl Illtroso'a ne- 1 Smoked sheets 100 100 100 100 These were mixed by mlllmg m the usual g ggggg ggg g g g g manner, care being taken, especlally wlth the g g; 3 3 g g g g compound of Formula I, to prevent prel1m1- Stearic an I a 3 a 5 nary vulcanlzation or scorchlng, The mlxed tfigggFQfiiitlfilf 9' compounds were then la1d in thin sheets in a amine 0 -5 0 Benzyl pheuyl mtroso 0 0 0.75 0 vulcanizing mold and vulcanized at- 20 Carbazol nitroso-amine 0 0 o 0.75 pounds steam pressure. Samples of each compound were vulcanized, for periods of 30, 7 and minutes, respectively. One portlon of each sample was then SUbJQCtBd to a tensile Final Final tensile elongastrength test, the results belng given ln the Stock Pmmdq 300% 500% lbslper mum fOHOWIIIg table. Mm. pressme sq. in. per cent We 1 a a 2:2 2 Cure at twenty pounds steam pressure 28 20 821 2200 9 8 2% 0 20 700 2020 0450 680 30 Minutes 20 04s 2250 3000 070 72 a a re 20 P 3 final 75 20 850 2230 3700 000 3007 500% sum 0 e ong a- P mm m 90 20 930 2400 3890 000 sq. in. I per cent 90 20 990 2600 3950 630 22 32s as as 1 A 735 1905 3400 685 D 90 II A 380 1140 2120 675 4 583 1075 2030 680 Table IV 45 Minutes A C D a 23 a! on no 300% 500% -p tion n Mineral rubber. 5 Q 5 5 5 sq- 111- P61 0811i Zinc oxide 5 6 5 5 s0 -0- 3 s 2 2 eanc 8C1 I A 958 4050 670 lliegcapto bgpfiolthiazolenn g8 $5 8.8 8.8

1 e snap y nitroso-amine.-. A 712 2000 3420 680 Phenyl beta-naphthyl nitroso- 0 0 o 75 0 amine A 948 M40 4125 675 Phenyl alpha naphthyl nitroso- A 010 2500 4150 075 amine 0 0 60 Minutes tFin il- IlFinal V Finel Final 40% 500% 53 5; 3,310;- Stock P d 500% 5 $53 51; 253%: sq. in. per cent Mi g z sq. in. per cent IV A 1120 2930 4280 6 5 I 75 20 850 \2200 3890 p 700 75 20 807 2300 3850 050 k s 1 -75 20 000 2005 3840 005 Y 75 20 840 me, 3700 555 Similar vulcanizmg experiments were cara ried out with composltlons containing other- 3:2 333 i892 5 00 20 985 2000 4000 055 mtroso amines, including both like and un 90 20 970. 2580 m 655 Same as Formula I with addition of 1.0 part diphenyl nitroso-amine.

III I Same as Formula I with addition of .7

radicals of both the aliphatic and aromatic series, as indicated in the above listin connection with the scorching test.

The experimental results are presented in the following tables:

, Table III Table V A B O D Smoked sheets 100 100 100 100 40 40 40 40 5 5 5 5 5 5 5 5 3 3 3 3 3 3 3 3 0. 8 0. 8 0. 8 0. 8 Diethy! nitroso-amine. i 0 0. 75 0 0 Piperidine nitroso-amine- 0 0 0. 75 0 Methyl phenyl nitroso-amine- 0 0 0 0. 75

C r are Final Final stock Pounds 300% as; are M111 pressure sq. in. per cent Table VI A B O D 100 100 100 100 40 40 4O 40 5 5 5 5 Zinc oxide. 5 5 5 5 Sulphun. 3 3 3 3 Stearic acid 3 3 3 3 Mercapto benzo thiazo1e. 0.8 0.8 0.8 0.8 Dialpha naphthyl nitroso-am1ne 0 0.75 0 0 Phenyl tolyl nitroso-amine 0 0 0.75 0 Ditolyl nitrosmamine 0 0 0 0. 75

Cure Final inal stock Pounds 300% 500% 132 5 5 $835; Min. pressure sq. in. per cent From the data thus obtained it ,is to be observed that, not only are the rubber compounds prepared with an addition of the diphenyl nitroso-amine, for example, free from the tendency toward preliminary vulcanization or scorching, but that when vulcanized at 20 pounds steam pressure and for the periods of time indicated, the vulcanized product exhibits as good or in some instances a superior cure (with respect to intermediate and final elongation values) than the compo sition to which such addition has not been made.

It is therefore shown that by means of this invention not only may extremely active accelerators, (which have been hitherto unavailable for use in the rubber industry on account of their very high activity) be safely employed in rubber compounds and mixed and milled without initiating premature vulcanization, but the vulcanized rubber product is initially as good or better than rubber similarly compounded and vulcanized but without the addition of an inhibiting reagent.

It is also indicated that whereas diaryl substituted nitroso-amines are especially effective, with respect to the prevention of premature acceleration of vulcanization, the alkyl or dialkyl substituted nitroso-amines may also be used, although somewhat less-effective.

Compounds which are in some respects related to the substituted nitroso-amines above defined, and have been thus tested for use in accordance with the invention, include carbazol nitroso-amine which may be spoken of as nitroso N-carbazol N.NO

Carbazol nitroso-amine or nitroso N-carbazol, however, is not strictly in the same category with the other compounds tested and in fact shows but little retarding efiect in the scorching test. The piperidine nitrosoamine likewise does not manifest pronounced retarding effects. The results are given, however, because they are related to the other nitroso-amine compounds. Their failure to be more effective in these respects may be attributed to the valence linkage between the R and R groups of the nitroso-amine; which will be apparent from the formula of the former compounds, as above given.

While the above disclosure relates to a preferred procedure, according to the invention, and to specific reagents employed in specific proportions, it is to be understood that variations may be made in both the mode of carrying out the invention and in the nature and amount of the several reagents used, according to the particular conditions of practics and the characteristics desired in the resulting product, as will be clear to those skilled in the art of treating rubber.

This application is a continuation in part of my application, Serial No. 323,556, filed December 3, 1928, and is designated as Case III-8 of a group of continuation applications filed on even date herewith.

I claim:

1. Method of vulcanizing rubber or rubber compositions with a vulcanizing agent and an organic accelerator characterized by controlling the action of the accelerator with an aryl paratolyl nitroso-amine,

2. Method of vulcanizing rubber or rubber compositions with a vulcamzing a ent and an organicaccelerator characterized y control ling the action of the accelerator with phenyl paratolyl nitroso-amine.

3. Method of vulcanizing rubberor rubber compositions with a vulcanizing agent and a sulphur-containing organic accelerator characterized by controlling the action of the accelerator with an aryl paratolyl nitrosoamine.

4. Method of vulcanizing rubber or rubber compositions with a vulcanizing agent and a sulphur-containing organic accelerator characterized by controlling the action of the accelerator with phenyl paratolyl nitrosoamine.

5. Method of vulcanizing rubber orr'ubber compositions with a vulcanizing agent and an accelerator containing a thiazole nucleus characterized by controlling the action of the accelerator with an aryl paratolyl nitrosoamine.

6. Method of vulcanizing rubber or rubber composltlons with a vulcanlzlng agent and an accelerator containing a thiazole nucleus characterized by controlling the action of the acceleratorwith phenyl paratolyl nitrosoamlne.

I 7. Method of vulcanizing rubber or rubber compositions with a vulcanizing agent and mercapto 'benzo thiazole characterized by controlling the action of the accelerator With an aryl paratolyl nitroso-amine.

8. Method of vulcanizing rubber or rubber composition with a vulcanizing agent and 'mercapto benzo thiazole characterized by controlling the action of the accelerator with phenyl paratolyl nitroso-amine.

9. An accelerator composition comprisin an organic accelerator and an aryl paratoly nitroso-amine.

10. An accelerator composition comprising an organic accelerator and phenyl paratoly nitroso-amin'e.

11. An accelerator composition comprisin a sulphur-containing organic accelerator an an aryl paratolyl nitroso-amine.

12. An accelerator composition comprising a sulphur-containing organic accelerator and phenyl paratolyl nitroso-amine.

13. An accelerator composition comprising an accelerator containing a thiazole nucleus and an aryl paratolyl nitroso-amine.

14:. An accelerator composition comprising an accelerator containing a thiazole nucleus and phenyl paratolyl nitroso-amine.

15. An accelerator composition comprising mercapto benzo thiazole and an aryl paratolyl nitroso-amine.

16. An accelerator composition comprising mercapto benzo thiazole and phenyl paratolyl nitroso-amine. 1

Signed by me at Boston, Massachusetts, this 1st day of June, 1929.

r H I-LENRY B. MORSE. 

